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26 Cards in this Set

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What are some of the characteristics of water?
-most abundant compound in most living things
-liquid at temperatures found over much of Earth
-expands as it freezes (unlike most substances)
Why does ice float on the surface of water?
ice is less dense than liquid water
polar molecule
a molecule in which the charges are unevenly distributed (the molecule is like a magnet with poles)

example: water molecule pg. 40
Why is a water molecule a polar molecule?
because there is an uneven distribution of electrons between the oxygen and hydrogen atoms

The negative pole is near the oxygen atom and the positive pole is between the hydrogen atoms.
Why are water molecules attracted to each other?
because of their partial positive and negative charges the molecules can attract to each other`
cohesion
an attraction between molecules of the same substance
-explains why drops of water form beads on a smooth surface
-explains why insects can walk on pond's surface
adhesion
an attraction between molecules of different substances
-explains why surface of water in cylinder diips in center
-causes water to rise in a narrow tube
capillary action
adhesion between water and glass causing water to rise in a narrow tube against the force of gravity
-draws water out of roots of plants and up stem to leaves
How do cohesion and adhesion help plants?
adhesion or capillary effect draws water out of roots and up stem

cohesion holds the column of water together as it rises
How are cohesion and adhesion similar ?

Different?
They are both an attraction between molecules.

Cohesion is an attraction between molecules of the same substance and adhesion is an attraction between molecules of different substances.
mixture
a material composed of two or more elements or compounds that are physically mixed together, but not chemically combined
ex. salt and pepper stirred together
solution
all the components are evenly distributed throughout the solution

ex. salt in a glass of water
solute
the substance that is dissolved
solvent
the substance in which the solute dissolves
Why is water the greatest solvent on Earth?
"Water's polarity gives it the ability to dissolve ionic compounds and other polar molecules."
suspension
mixture of water and nondissolved materials
Why is water neutral?
"Because the number of positive hydrogen ions produced is equal to the number of negative hydroxide ions produced."
pH scale
a measurement system which indicates the concentration of H+ ions in solution

scale ranges from 0 -14
Explain the pH scale.
At a pH of 7, the concentration of H+ ions and OH- ions is equal. Pure water has pH of 7.
Below 7 are called acidic because they have more H+ ions than OH- ions.
Above 7 are called basic because they have more OH- ions than H+ ions
What does each step on the pH scale represent?
Each step on the pH scale represents a factor of 10

ex. solution w/pH of 4 has 10 times as many H+ ions as a liter of a solution w/pH of 5
What is an acid?
An acid is any compound that forms H+ ions in solution
What do acidic solutions contain?
Higher concentrations of H+ ions than pure water and have pH values below 7
base
a compound that produces hydroxide ions (OH- ions) in solution
What do basic, or alkaline, solutions contain?
Lower concentrations of H+ ions than pure water and have pH values above 7
buffers
weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH
why must the pH of the fluids within most cells in the human body be kept between 6.5 and 7.5?
Higher or lower pH will affect the chemical reactions that take place within the cells.
Important for maintaining homeostasis
Controls using buffers to prevent sudden pH changes.